WO2018064722A1 - Piezoelectric contact sensor - Google Patents

Piezoelectric contact sensor Download PDF

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Publication number
WO2018064722A1
WO2018064722A1 PCT/AU2017/051084 AU2017051084W WO2018064722A1 WO 2018064722 A1 WO2018064722 A1 WO 2018064722A1 AU 2017051084 W AU2017051084 W AU 2017051084W WO 2018064722 A1 WO2018064722 A1 WO 2018064722A1
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WO
WIPO (PCT)
Prior art keywords
contact sensor
conductive
forming
piezoelectric
piezoelectric material
Prior art date
Application number
PCT/AU2017/051084
Other languages
French (fr)
Inventor
Sean Suixiang LI
Dewei CHU
Danyang Wang
Original Assignee
Newsouth Innovations Pty Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2016904049A external-priority patent/AU2016904049A0/en
Application filed by Newsouth Innovations Pty Limited filed Critical Newsouth Innovations Pty Limited
Publication of WO2018064722A1 publication Critical patent/WO2018064722A1/en

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Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/30—Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
    • H10N30/302—Sensors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/07—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base
    • H10N30/074—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base by depositing piezoelectric or electrostrictive layers, e.g. aerosol or screen printing
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2203/00—Indexing scheme relating to G06F3/00 - G06F3/048
    • G06F2203/041—Indexing scheme relating to G06F3/041 - G06F3/045
    • G06F2203/04103—Manufacturing, i.e. details related to manufacturing processes specially suited for touch sensitive devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/853—Ceramic compositions
    • H10N30/8536—Alkaline earth metal based oxides, e.g. barium titanates
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/853—Ceramic compositions
    • H10N30/8542—Alkali metal based oxides, e.g. lithium, sodium or potassium niobates
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/853—Ceramic compositions
    • H10N30/8561—Bismuth-based oxides

Definitions

  • a contact sensor is disclosed.
  • a method of manufacturing a contact sensor is also disclosed.
  • the contact sensor disclosed may find particular application in touchscreen panels, although is not limited to touchscreen panels.
  • the method of manufacturing a contact sensor may provide a simplified manufacturing method that allows patterning and deposition of various components to be achieved using low-cost, readily available technologies that do not place size constraints on the manufactured sensor or resulting touchscreen.
  • touchscreens can be generally classified into two different types: resistive; or capacitive.
  • Resistive -type touchscreens are relatively simple, with a low manufacturing cost.
  • each panel i.e. the panel that a user touches
  • a lower generally inflexible panel that are separated by a small predetermined gap.
  • the inner surface of each panel i.e. the surfaces between which the gap is formed
  • a thin conductive layer When a user contacts the flexible input panel, it deflects and contacts the lower panel, resulting in electrical flow.
  • they use significant amounts of power as electrical current needs to be applied across both conductive layers, regardless of whether the input panel is being touched. Because of the deformation of the input panel, it is subject to easy aging, thus reducing the longevity of the device.
  • the resolution of resistive -type touchscreens is relatively low, and multi-touch detection is not generally supported.
  • Capacitive-type touchscreens detect a contact position on the screen by identifying when a decrease in capacitance of the screen has occurred. They have a single substrate with an electrode layer, and a thin protective film. When a user touches the screen with an exposed finger, or a stylus holding an electrical charge, some of the electrical charge from the screen electrode transfers to the user. It is this decrease in capacitance that is identified.
  • Capacitive-type touchscreens have many advantages over resistive-type touchscreens, such as supporting multi-touch detection, better image resolution and lower power consumption. However, they can be somewhat inaccurate due to so-called 'ghost clicks' caused by contaminants or moisture on the surface inducing static electricity (which reduces the capacitance at that point).
  • Formation of the conductive or electrode layers for either capacitive or resistive touchscreens can be quite complicated as multiple, distinct processing stages are required. For example, deposition and patterning of the conductive or electrode layers need to be conducted separately. A common technique used to achieve this is physical vapour deposition (PVD), whereby a layer of the conductive or electrode material is deposited onto a substrate. In such a technology, the size of the substrates will be often limited by the complex and expensive vacuum chambers. The unwanted regions of the conductive or electrode material are then removed using laser cutting/irradiating, lithography or etching techniques, leaving the desired patterning of the conductive or electrode material on the substrate.
  • PVD physical vapour deposition
  • Piezoelectric materials are materials that generate an electrical potential when they are mechanically stressed (i.e. when they are compressed), or change their crystallographic spacing when an electrical field is applied.
  • lead-based piezoelectric materials have been the most widely utilised piezoelectric materials for touchscreens due to their high piezoelectric coefficients (amount of electrical charge generated per applied force unit). See, for example, US20120075221.
  • due to environmental concerns associated with the use of lead because of its toxicity, many countries have introduced restrictions on its use, particularly in electrical and electronic equipment which have relatively short product-lives.
  • Organic piezoelectric materials are emerging as alternative technology to the lead- based piezoelectric materials. See, for example, WO2014/037016. However, organic piezoelectric materials have a much lower piezoelectric coefficient than lead-based materials. Additionally, organic piezoelectric materials are more susceptible to UV radiation than lead- based materials. This can result in degradation when the material is exposed to UV radiation, such as when being used outdoors, reducing longevity of the material and, ultimately, the product in which it is used.
  • the above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the contact sensor, method of manufacturing a contact sensor and composition as disclosed herein.
  • a contact sensor may detect when part of the sensor is touched.
  • the contact sensor may find particular application in a variety of touchscreen technologies including, but not limited to, smart phones, tablets, laptops, computers, automobile navigation systems, bank automatic teller machines (ATMs), industrial control systems, medical devices, ticket vending machines, etc. It should also be appreciated that the contact sensor disclosed herein may find application in technologies not previously envisaged, due to its ability to be cost-effectively produced on a larger scale than known technologies.
  • the contact sensor comprises a first substrate.
  • the first substrate may include condensed matter materials such as glass, silicon, polymers (e.g. polyimide, polyester, etc.), composites or another insulating material.
  • the first substrate may be relatively rigid or relatively flexible, depending on the intended application.
  • the contact sensor also comprises a first conductive layer, a sensing layer and a second conductive layer.
  • the sensing layer is essentially sandwiched between the two conductive layers.
  • the first conductive layer may be the same as, or similar to, the second conductive layer, although it should be appreciated that the first and second conductive layers may be different. Employing the same first and second conductive layers may simplify the production of such contact sensors, and ensure consistent electrical properties in the contact sensor.
  • the first and/or second conductive layers may include first and/or second conductive materials.
  • the conductive material may include a variety of transparent conductive oxide materials, such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), and some conductive polymers and graphene/graphene oxide.
  • transparent conductive oxide materials such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), and some conductive polymers and graphene/graphene oxide.
  • transparent conductive oxide materials may be deposited onto the first substrate utilising relatively simple techniques such as various printing processes. This can allow contact sensors and, therefore, touchscreen panels significantly larger than known touchscreens to be
  • the transparent conductive oxide materials may be quantum oxide dots.
  • the sensing layer includes a piezoelectric material.
  • the use of a piezoelectric material in the contact sensor means that the mere act of contacting (e.g. touching) the sensor will be sufficient to obtain an electrical signal, and the sensor is not reliant on contact with human skin (or other object that results in capacitance changes), as capacitive-type touchscreens are.
  • the contact sensor disclosed herein will facilitate a touchscreen panel that can sense (detect) contact therewith by any object (e.g. fingernail, pen, stylus, gloved finger, etc.).
  • the contact sensor disclosed herein may support multi-contact detection.
  • the contact sensor disclosed herein may provide the desired features of both the resistive-type and capacitive-type touchscreens, whilst avoiding their respective shortcomings.
  • piezoelectric materials may be sufficiently sensitive to not only sense (detect) the location of the contact, but to also determine with how much force said contact was made. In the context of touchscreen panels for so-called 'smart' devices, this may assist in determining the type of contact being made (e.g. more forceful contact may result in a particular control output). Further, tactile feedback may be provided for particular contact forces.
  • the piezoelectric material may be a lead-free piezoelectric material. This is contrary to most piezoelectric based touchscreen systems, and offers environmental benefits.
  • the piezoelectric material may alternatively or additionally be an inorganic piezoelectric material. Inorganic piezoelectric materials will usually have a higher piezoelectric coefficient (approximately one order of magnitude higher) than organic (e.g. polymer-based) piezoelectric materials. The piezoelectric coefficient describes the amount of electrical charge generated per applied force unit. As such, materials with higher piezoelectric coefficients will generate more electrical charge, resulting in a contact sensor with higher sensitivity and more accuracy.
  • the piezoelectric material may have a perovskite-type lattice structure.
  • the perovskite-type lattice structure is a relatively simple crystal structure, which contributes to the higher piezoelectric coefficients in materials with such a structure.
  • the piezoelectric material may be one or more of: (Bi,Na)TiC> 3 ; (Ba,Ca)(Ti,Zr)0 3 ; or (K,Na)Nb0 3 .
  • the first conductive layer may comprise two or more substantially parallel rows of a first conductive material. In this manner, each row of the first conductive material may form an electrode.
  • the second conductive layer may comprise two or more substantially parallel columns of a second conductive material. Similarly, in this manner each column of the second conductive material may form an electrode.
  • the rows of the first conductive material may be substantially perpendicular to the columns of the second conductive material.
  • the rows of the first conductive material and the columns of the second conductive material may at least partially intersect to form a hatched pattern.
  • the rows and columns may form a cross-hatched pattern.
  • the sensing layer may comprise a plurality of discrete regions of the piezoelectric material.
  • the discrete regions of the piezoelectric material may substantially correspond to the regions at which the rows of the first conductive material and the columns of the second conductive material intersect. In this way, each discrete region of piezoelectric material is independent from each other discrete region, allowing contact to be sensed (i.e. detected) with a high degree of accuracy.
  • the sensing layer may further comprise an insulating material surrounding the discrete regions of piezoelectric material.
  • Suitable insulating materials may include condensed matter materials such as inorganic materials (e.g. S1O 2 , AI 2 O 3 , S1 3 N4 or other inorganic materials), organic materials (e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials), composites or a combination thereof. This can assist in further isolating the discrete regions of piezoelectric material and improve accuracy of the contact sensor.
  • inorganic materials e.g. S1O 2 , AI 2 O 3 , S1 3 N4 or other inorganic materials
  • organic materials e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials
  • the contact sensor may further comprise a second substrate, for example in the form of a cover.
  • the type of cover such as the material or format of the cover, may be dependent on the intended use of the contact sensor.
  • the cover may further comprise key pads to specifically identify regions of the contact sensor to be contacted.
  • the cover may be a thin panel or sheet, such as a thin film or glass sheet. This cover may protect the first conductive layer, sensing layer and second conductive layer from damage, and be the material that a user contacts (i.e. touches) when utilising the contact sensor disclosed herein.
  • first substrate, first conductive layer, sensing layer and second conductive layer may be substantially transparent. This may be dependent on the intended application of the contact sensor.
  • each of the first substrate, first conductive layer, sensing layer and second conductive layer may be substantially transparent in contact sensors for smart phone, tablet, laptop, etc., touchscreens.
  • a contact sensor is disclosed.
  • the contact sensor comprises a first insulating substrate, a first conductive layer, a sensing layer and a second conductive layer.
  • the sensing layer comprises an inorganic lead-free piezoelectric material.
  • the contact sensor of the second aspect may be otherwise as defined above in the first aspect.
  • a method of manufacturing a contact sensor comprises providing a first substrate and forming a first conductive layer on the first substrate.
  • the method also comprises forming a sensing layer comprising a piezoelectric material, and forming a second conductive layer.
  • the piezoelectric material may be a lead-free piezoelectric material.
  • the piezoelectric material may alternatively or additionally be an inorganic piezoelectric material, which usually has a higher piezoelectric coefficient (approximately one order of magnitude higher) than organic (e.g. polymer-based) piezoelectric materials.
  • the piezoelectric coefficient describes the amount of electrical charge generated per applied force unit. As such, materials with higher piezoelectric coefficients will generate more electrical charge, resulting in a contact sensor with higher sensitivity and more accuracy.
  • the piezoelectric material may have a perovskite-type lattice structure.
  • the perovskite-type lattice structure is a relatively simple crystal structure, which contributes to the higher piezoelectric coefficients in materials with such a structure.
  • the piezoelectric material may be one or more of: (Bi,Na)TiC>3; (Ba,Ca)(Ti,Zr)03; or (K,Na)Nb0 3 .
  • a second substrate may be provided, such that the first conductive layer, sensing layer and second conductive layer are positioned between the first and second substrates.
  • the second substrate may, in some forms, be in the form of a cover.
  • the type of cover such as the material or format of the cover, may be dependent on the intended use of the contact sensor.
  • the cover may further comprise key pads to specifically identify regions of the contact sensor to be contacted.
  • the cover may be a thin panel or sheet, such as a thin film or glass sheet. This cover may protect the first conductive layer, sensing layer and second conductive layer from damage, and be the material that a user contacts (i.e. touches) when utilising the contact sensor disclosed herein.
  • the second conductive layer may be formed on the second substrate.
  • the first and/or second substrate may be cleaned or otherwise treated to improve the wettability of its surface.
  • the substrate may be UV-treated to reduce its surface energy. It should be appreciated that other surface treatments may be employed to achieve improved wettability, and such surface treatment may be dependent on the type of substrate employed (e.g. glass, polyimide, polyester, etc.).
  • the sensing layer may be formed on the first conductive layer (i.e. on the first conductive layer which has been formed on the first substrate). In other forms, the sensing layer may be formed on the second conductive layer (i.e. on the second conductive layer which has been formed on the second substrate). In yet other forms, some of the sensing layer may be formed on the first conductive layer (i.e. first substrate) and some of the sensing layer may be formed on the second conductive layer (i.e. second substrate), with the two halves being combined to form the contact sensor.
  • the first conductive layer may comprise two or more substantially parallel rows of a first conductive material. In this manner, each row of the first conductive material may form an electrode.
  • the second conductive layer may comprise two or more substantially parallel columns of a second conductive material. Similarly, in this manner each column of the second conductive material may form an electrode.
  • first and second conductive materials may be the same materials.
  • the conductive material may include a variety of transparent conductive oxide materials, such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), and some conductive polymers.
  • ITO indium tin oxide
  • FTO fluorine-doped tin oxide
  • AZO aluminium-doped zinc oxide
  • BZO boron-doped zinc oxide
  • SRO strontium ruthenium oxide
  • Such transparent conductive oxide materials may be deposited onto the first substrate utilising relatively simple techniques such as various printing processes. This can allow contact sensors and, therefore, touchscreen panels significantly larger than known touchscreens to be manufactured.
  • the transparent conductive oxide materials may be quantum oxide dots, and may be in the form of an ink as disclosed in co-pending PCT application number PCT/AU2016/050686, by the present applicant.
  • the rows of the first conductive material may be substantially perpendicular to the columns of the second conductive material.
  • the rows of the first conductive material and the columns of the second conductive material may at least partially intersect to form a hatched pattern.
  • the rows and columns may form a cross-hatched pattern.
  • a plurality of discrete regions of the piezoelectric material may be formed, thereby forming the sensing layer.
  • the discrete regions of the piezoelectric material may be formed to substantially correspond to the regions at which the rows of the first conductive material and the columns of the second conductive material intersect. In this way, each discrete region of piezoelectric material is independent from each other discrete region, allowing contact to be sensed (i.e. detected) with a high degree of accuracy.
  • forming the sensing layer may further comprise surrounding the discrete regions of piezoelectric material with an insulating material.
  • Suitable insulating materials may include condensed matter materials such as inorganic materials (e.g. S1O 2 , AI 2 O 3 , S1 3 N4 or other inorganic materials), organic materials (e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials), composites or a combination thereof. This can assist in further isolating the discrete regions of piezoelectric material and improve accuracy of the contact sensor.
  • inorganic materials e.g. S1O 2 , AI 2 O 3 , S1 3 N4 or other inorganic materials
  • organic materials e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials
  • forming the sensing layer may further comprise annealing the piezoelectric material.
  • Annealing the piezoelectric material may improve its crystallinity and piezoelectric properties. Annealing may be conducted at a temperature between
  • the substrates may be different materials.
  • One of the substrate materials may have properties making it more suitable to undergo annealing.
  • the piezoelectric material may be formed on the conductive layer on that substrate (e.g. the second conductive layer may be formed on the second substrate, or the first conductive layer may be formed on the first substrate, with the piezoelectric material being subsequently formed thereon).
  • the piezoelectric material may be annealed prior to being surrounded with the insulating material. This may be preferred when the insulating material has a low melting temperature, to avoid its structure from undergoing any significant transformation (e.g. which may result in an otherwise transparent material becoming cloudy and opaque).
  • the first conductive layer, the sensing layer, the second conductive layer may be formed by any suitable process.
  • the respective layers may be formed by one or more of: ink-jet printing; spray printing; spin-coating; slot die coating; doctor blade coating; knife printing; screen-printing/coating; gravure printing/coating; engraved roller
  • each respective layer may be formed by the same process, or a different process.
  • each of the piezoelectric material and insulating material may be formed by one of the processes identified above.
  • Various embodiments of the method disclosed herein may provide a low-cost manufacturing method whereby patterning and deposition of various components of the contact sensor can be achieved using low-cost, readily available technologies that do not place size constraints on the manufactured sensor.
  • Various embodiments may also provide a method that eliminates the requirement of laser cutting, irradiation, or adhesion layers which may adversely affect properties of the substrate and/or contact sensor.
  • a composition comprising a lead-free piezoelectric material dispersed in a solvent.
  • the composition may be utilised as an ink in the printing of lead-free piezoelectric materials.
  • the ink may be applied using: ink-jet printing; spray printing; spin-coating; slot die coating; doctor blade coating; knife printing; screen-printing/coating; gravure printing/coating; engraved roller printing/coating; comma-bar printing/coating; micro-roller printing/coating; nano-imprint printing; bar spreading; dip-coating; contact coating; non-contact coating; or a combination thereof.
  • the piezoelectric material may alternatively or additionally be an inorganic piezoelectric material.
  • the piezoelectric material may have a perovskite-type lattice structure.
  • the piezoelectric material may be one or more of:
  • composition disclosed in this fourth aspect may be utilised in the method of manufacturing a contact sensor as defined in the third aspect, or may be used to form the piezoelectric material of the sensing layer as defined in the first and second aspects.
  • Figure 1 shows an exploded schematic illustration of an embodiment of a contact sensor according to the present disclosure
  • Figure 2 shows a schematic top view illustration of an embodiment of a contact sensor, as shown in Figure 1 ;
  • Figure 3A shows a cross-sectional schematic illustration, taken along line A-A, of the contact sensor shown in Figure 2;
  • Figure 3B shows a cross-sectional schematic illustration, taken along line B-B, of the contact sensor shown in Figure 2;
  • Figure 4 shows an exploded schematic illustration of an alternative embodiment of a contact sensor according to the present disclosure
  • Figure 5 shows an exploded schematic illustration of an alternative embodiment of a contact sensor according to the present disclosure
  • Figure 6 shows a schematic top view illustration of an embodiment of a contact sensor, as shown in Figure 5;
  • Figure 7A shows a cross-sectional schematic illustration, taken along line A-A, of the contact sensor shown in Figure 6;
  • Figure 7B shows a cross-sectional schematic illustration, taken along line B-B, of the contact sensor shown in Figure 6;
  • Figure 8 shows an exploded schematic illustration of an alternative embodiment of a contact sensor according to the present disclosure
  • Figure 9 shows the optical transmission spectrum of a piezoelectric thin film deposition on ITO coated glass substrate
  • Figure 10 shows a piezoelectric response butterfly loop of a typical perovskite- structured piezoelectric thin film
  • Figure 11 shows a cross-sectional TEM image of a typical perovskite-structured piezoelectric thin film
  • Figure 12 shows a ferroelectric P-E hysteresis loop a typical perovskite-structured piezoelectric thin film
  • Figure 13 shows a frequency-dependent dielectric constant of a typical perovskite- structured piezoelectric thin film.
  • FIG. 1 a general exploded schematic illustration of an embodiment of a contact sensor is shown.
  • the contact sensor is in the form of a touchscreen panel 100.
  • Touchscreen panels may find particular application in smart phones, tablets, laptops, computers, automobile navigation systems, bank automatic teller machines (ATMs), industrial control systems, medical devices, ticket vending machines, etc.
  • ATMs bank automatic teller machines
  • the piezoelectric touchscreen panel 100 is shown having four rows 101 of a first conducting material, forming the first (or lower) conducting layer 102 on a substrate 104.
  • the first conducting material may include indium tin oxide (ITO), or one of the other conducting materials disclosed in the Summary, such as fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers.
  • the substrate 104 may be composed of condensed matter materials such as glass, silicon, polymers (e.g. polyimide, polyester, etc.), composites or another insulating material.
  • a sensing layer 106 comprising an array of discrete regions of piezoelectric material 108 embedded in an insulating material 110.
  • the piezoelectric material in the illustrated form may be an inorganic, lead-free piezoelectric material having a perovskite-type lattice structure, such as (Bi,Na)Ti03, (Ba,Ca)(Ti,Zr)0 3 , or (K,Na)Nb0 3 .
  • the insulating material 110 may include inorganic materials (e.g. S1O 2 , AI 2 O 3 , S1 3 N4 or other inorganic materials), organic materials (e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials), composites or a combination thereof.
  • the piezoelectric touchscreen panel 100 is also shown having four columns of a second conducting material, forming the second (or upper) conducting layer 112.
  • the second conducting material may comprise indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers.
  • the first and second conducting materials are the same, such as ITO. However in alternative embodiments the conducting materials may differ from one another.
  • the piezoelectric touchscreen panel 100 comprises a second substrate, in the form of a cover or screen 114.
  • the screen 114 is the part of the touchscreen 100 that a user will contact.
  • each row of the first conducting material in the first conducting layer 102 is substantially parallel to adjacent rows.
  • each column of the second conducting material in the second conducting layer 112 is substantially parallel to adjacent columns.
  • each row in the first conducting layer 102 is substantially perpendicular to each column in the second conducting layer 112, forming the hatched pattern (i.e. cross-hatched pattern) shown in Figure 2.
  • Figure 2 also best shows the relative placement of the discrete regions of piezoelectric material 108 with respect to the first (lower) conducting layer 102 and the second (upper) conducting layer 112.
  • the discrete regions of piezoelectric material 108 are shown positioned at the points 114 that rows of the first conducting layer 102 and columns of the second conducting layer 112 intersect or overlap.
  • the sensing layer 106 (discrete regions of piezoelectric material 108 embedded in an insulating material 110) is depicted in Figure 2 as terminating before each edge of the substrate 104. It should be appreciated that the sensing layer 106 may extend to each edge of the substrate, as depicted in Figures 3A and 3B, and that the sensing layer 106 may only be depicted in this manner in Figure 2 to assist with interpretation (e.g. due to the schematic being a two-dimensional representation).
  • glass substrate 104 may be treated, such as by UV irradiation, to improve the wettability of its surface by reducing its surface energy.
  • a first ink comprising ITO quantum oxide dots dispersed in a solvent, may be used to print, such as by ink-jet printing, the rows of the first conducting layer 102 onto the glass substrate 104.
  • a second ink comprising a lead-free piezoelectric material dispersed in a solvent
  • a second ink may be used to print, such as by ink-jet printing, discrete regions of piezoelectric material 108 onto specific regions of the first conducting layer 102.
  • the discrete regions of piezoelectric material 108 are allowed to dry, and then the substrate is heated to anneal the piezoelectric material to improve its crystallinity and piezoelectric properties.
  • a third ink comprising polyethylene terephthalate (PET) may be used to print, such as by ink-jet printing, the PET (i.e. insulating material 110) into the spacing surrounding the discrete regions of piezoelectric material 108, thereby embedding the piezoelectric material 108 in the insulating material 110 to form the sensing layer 106.
  • PET polyethylene terephthalate
  • the first ink comprising ITO quantum oxide dots dispersed in a solvent
  • the first ink can again be used to print, such as by ink-jet printing, the conductive material to continue forming the sensor.
  • the first ink is used to print columns, that are perpendicular to the first conducting layer 102 and that overlie the discrete regions of piezoelectric material 108, of the second conducting layer 112 onto the sensing layer 106.
  • Insulating material 110 electrically isolates the first conducting layer 102 from the second conducting layer 112, other than at the discrete regions of piezoelectric material 108 which are used to detect contact therewith.
  • a second substrate in the form of a thin-film cover or screen 114, is provided on top of the second conducting layer 112, thereby forming the piezoelectric touchscreen 100.
  • each of the rows of the first conducting layer 102, and each of the columns of the second conducting layer 112 may be electrically connected to a controller or a logic unit.
  • Piezoelectric touchscreen 200 is essentially identical to the piezoelectric touchscreen 100 depicted in Figure 1 except for screen 212.
  • piezoelectric touchscreen 200 is also shown having four rows of a first conducting material, such as ITO, forming the first (or lower) conducting layer 202 on a substrate, such as glass, 204.
  • a sensing layer 206 is also shown comprising an array of discrete regions of piezoelectric material 208 embedded in an insulating material 210.
  • screen 214 is shown having "key pads" 216 positioned to overlie the array of discrete regions of piezoelectric material 208 (i.e. above those regions of the second conducting layer 212 which overlie the discrete regions of piezoelectric material 208, when assembled).
  • Such an arrangement may be useful for a relatively static system that only requires or allows a specific configuration of touches on the screen to be recognised.
  • Figures 5 through 7 an alternative embodiment of a contact sensor in the form of a touchscreen panel 300 is shown.
  • the panel 300 comprises a first or lower layer 301 having a layer of conducting material 302 on a substrate 304.
  • the layer of conducting material 302 extends across the substrate 304.
  • the conducting material may be located in stripes or sections or in any layout that suits the purpose.
  • a sensing layer 306 comprising a layer of piezoelectric material 308 embedded in an insulating material 310.
  • the conducting layer is in the form of discrete deposits of a conducting material.
  • the material may comprise indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron- doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers.
  • the piezoelectric touchscreen panel 300 comprises a second substrate, in the form of a cover or screen 314.
  • the screen 314 is the part of the touchscreen 300 that a user will contact.
  • the contact sensor of this embodiment may in some forms include a plurality of keypads or buttons 316 adapted to allow user contact.
  • the upper contact layer includes a plurality of keypads or buttons 416.
  • the panel 400 comprises a first or lower layer 401 having a layer of conducting material 402 on a substrate 404.
  • the layer of conducting material 402 extends across the substrate 404.
  • the conducting material may be located in stripes or sections or in any layout that suits the purpose.
  • a sensing layer 406 comprising a layer of piezoelectric material 408 embedded in an insulating material 410.
  • the conducting layer is in the form of discrete deposits of a conducting material.
  • the material may comprise indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron- doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers.
  • the piezoelectric touchscreen panel 400 comprises a second substrate, in the form of a cover or screen 414.
  • the screen 414 is the part of the touchscreen 400 that a user will contact.
  • piezoelectric thin films including perovskite oxides (e.g. (Bi, Na)Ti03; (Ba, Ca)(Ti, Zr)03; or (K, Na)Nb03), and more are deposited or printed on the indium tin oxide (ITO) coated substrates, such as glass, PET and others with non-contact methods such as Physical Vapor Deposition (e.g., RF sputtering, thermal evaporation, e-gun evaporation, pulsed laser deposition and more), Chemical Vapor Deposition (e.g. atomic layer deposition, MOCVD, PECVD and more), spin coating and various printing technologies and others, for Proof of Concept. These thin films are transparent in the wavelength range of 400 nm to 1000 nm.
  • ITO indium tin oxide
  • FIG. 9 A typical transmittance spectra measured from the sample fabricated in our lab with RF sputtering technology is shown in Figure 9, which shows the resulting optical transmission spectrum of a piezoelectric thin film deposition on ITO coated glass substrate. This demonstrates that the optical clarity is satisfactory for the requirements of the applications, such as use in touchscreens etc.
  • the cross-sectional TEM image shown in Figure 11 clearly shows the thickness of this sample is around 300 nm.
  • the robust ferroelectric activity of this sample is confirmed by its well-defined P-E hysteresis as shown in Figure 12.
  • This sample also possesses high dielectric constant at low frequencies, i.e. ⁇ ⁇ 100 kHz, as shown in Figure 13.

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Abstract

A contact sensor comprising a first conductive layer; a sensing layer comprising a piezoelectric material, and a second conductive layer. An embodiment includes piezoelectric material that is lead free and selected from: (Bi,Na)TiO3; (Ba,Ca)(Ti,Zr)O3; or (K,Na)NbO3. The method of manufacture is low-cost preferably using a printing/coating technique that does not place size constraints on the manufactured sensor.

Description

PIEZOELECTRIC CONTACT SENSOR
Technical Field
A contact sensor is disclosed. A method of manufacturing a contact sensor is also disclosed. The contact sensor disclosed may find particular application in touchscreen panels, although is not limited to touchscreen panels. The method of manufacturing a contact sensor may provide a simplified manufacturing method that allows patterning and deposition of various components to be achieved using low-cost, readily available technologies that do not place size constraints on the manufactured sensor or resulting touchscreen. Background Art
With the increased consumer reliance on touchscreen devices, such as smart phones, tablets, laptops, etc., accuracy and sensitivity of touchscreens is becoming more important. Commonly used touchscreens can be generally classified into two different types: resistive; or capacitive.
Resistive -type touchscreens are relatively simple, with a low manufacturing cost.
They have an upper flexible input panel (i.e. the panel that a user touches) and a lower generally inflexible panel that are separated by a small predetermined gap. The inner surface of each panel (i.e. the surfaces between which the gap is formed) is coated with a thin conductive layer. When a user contacts the flexible input panel, it deflects and contacts the lower panel, resulting in electrical flow. However, they use significant amounts of power as electrical current needs to be applied across both conductive layers, regardless of whether the input panel is being touched. Because of the deformation of the input panel, it is subject to easy aging, thus reducing the longevity of the device. Furthermore, the resolution of resistive -type touchscreens is relatively low, and multi-touch detection is not generally supported.
Capacitive-type touchscreens detect a contact position on the screen by identifying when a decrease in capacitance of the screen has occurred. They have a single substrate with an electrode layer, and a thin protective film. When a user touches the screen with an exposed finger, or a stylus holding an electrical charge, some of the electrical charge from the screen electrode transfers to the user. It is this decrease in capacitance that is identified.
Capacitive-type touchscreens have many advantages over resistive-type touchscreens, such as supporting multi-touch detection, better image resolution and lower power consumption. However, they can be somewhat inaccurate due to so-called 'ghost clicks' caused by contaminants or moisture on the surface inducing static electricity (which reduces the capacitance at that point).
Formation of the conductive or electrode layers for either capacitive or resistive touchscreens can be quite complicated as multiple, distinct processing stages are required. For example, deposition and patterning of the conductive or electrode layers need to be conducted separately. A common technique used to achieve this is physical vapour deposition (PVD), whereby a layer of the conductive or electrode material is deposited onto a substrate. In such a technology, the size of the substrates will be often limited by the complex and expensive vacuum chambers. The unwanted regions of the conductive or electrode material are then removed using laser cutting/irradiating, lithography or etching techniques, leaving the desired patterning of the conductive or electrode material on the substrate. Laser cutting/irradiating can adversely affect the mechanical properties of the substrate, which can lead to the generation of micro-cracks and subsequent failure of the touchscreen. Furthermore, it may be necessary to use adhesion layers to ensure adhesion of the conductive or electrode material to the substrate. Such adhesion layers are in addition to the conductive and electrode materials, and require additional resources and additional steps during manufacture. The use of adhesion layers, and the processing steps required for lithography and etching, can greatly increase the complexity of the manufacturing process.
Piezoelectric materials are materials that generate an electrical potential when they are mechanically stressed (i.e. when they are compressed), or change their crystallographic spacing when an electrical field is applied. To date, lead-based piezoelectric materials have been the most widely utilised piezoelectric materials for touchscreens due to their high piezoelectric coefficients (amount of electrical charge generated per applied force unit). See, for example, US20120075221. However, due to environmental concerns associated with the use of lead because of its toxicity, many countries have introduced restrictions on its use, particularly in electrical and electronic equipment which have relatively short product-lives.
Organic piezoelectric materials are emerging as alternative technology to the lead- based piezoelectric materials. See, for example, WO2014/037016. However, organic piezoelectric materials have a much lower piezoelectric coefficient than lead-based materials. Additionally, organic piezoelectric materials are more susceptible to UV radiation than lead- based materials. This can result in degradation when the material is exposed to UV radiation, such as when being used outdoors, reducing longevity of the material and, ultimately, the product in which it is used. The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the contact sensor, method of manufacturing a contact sensor and composition as disclosed herein.
Summary
According to a first aspect, a contact sensor is disclosed. In this regard, the contact sensor may detect when part of the sensor is touched. The contact sensor may find particular application in a variety of touchscreen technologies including, but not limited to, smart phones, tablets, laptops, computers, automobile navigation systems, bank automatic teller machines (ATMs), industrial control systems, medical devices, ticket vending machines, etc. It should also be appreciated that the contact sensor disclosed herein may find application in technologies not previously envisaged, due to its ability to be cost-effectively produced on a larger scale than known technologies.
The contact sensor comprises a first substrate. The first substrate may include condensed matter materials such as glass, silicon, polymers (e.g. polyimide, polyester, etc.), composites or another insulating material. The first substrate may be relatively rigid or relatively flexible, depending on the intended application.
The contact sensor also comprises a first conductive layer, a sensing layer and a second conductive layer. The sensing layer is essentially sandwiched between the two conductive layers. The first conductive layer may be the same as, or similar to, the second conductive layer, although it should be appreciated that the first and second conductive layers may be different. Employing the same first and second conductive layers may simplify the production of such contact sensors, and ensure consistent electrical properties in the contact sensor. The first and/or second conductive layers may include first and/or second conductive materials. For example, the conductive material may include a variety of transparent conductive oxide materials, such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), and some conductive polymers and graphene/graphene oxide. Such transparent conductive oxide materials may be deposited onto the first substrate utilising relatively simple techniques such as various printing processes. This can allow contact sensors and, therefore, touchscreen panels significantly larger than known touchscreens to be
manufactured. The transparent conductive oxide materials may be quantum oxide dots. The sensing layer includes a piezoelectric material. The use of a piezoelectric material in the contact sensor means that the mere act of contacting (e.g. touching) the sensor will be sufficient to obtain an electrical signal, and the sensor is not reliant on contact with human skin (or other object that results in capacitance changes), as capacitive-type touchscreens are. Thus, the contact sensor disclosed herein will facilitate a touchscreen panel that can sense (detect) contact therewith by any object (e.g. fingernail, pen, stylus, gloved finger, etc.). Furthermore, in some forms the contact sensor disclosed herein may support multi-contact detection. In this regard, the contact sensor disclosed herein may provide the desired features of both the resistive-type and capacitive-type touchscreens, whilst avoiding their respective shortcomings.
Additionally, piezoelectric materials may be sufficiently sensitive to not only sense (detect) the location of the contact, but to also determine with how much force said contact was made. In the context of touchscreen panels for so-called 'smart' devices, this may assist in determining the type of contact being made (e.g. more forceful contact may result in a particular control output). Further, tactile feedback may be provided for particular contact forces.
In some forms, the piezoelectric material may be a lead-free piezoelectric material. This is contrary to most piezoelectric based touchscreen systems, and offers environmental benefits. In some forms, the piezoelectric material may alternatively or additionally be an inorganic piezoelectric material. Inorganic piezoelectric materials will usually have a higher piezoelectric coefficient (approximately one order of magnitude higher) than organic (e.g. polymer-based) piezoelectric materials. The piezoelectric coefficient describes the amount of electrical charge generated per applied force unit. As such, materials with higher piezoelectric coefficients will generate more electrical charge, resulting in a contact sensor with higher sensitivity and more accuracy.
In some forms, the piezoelectric material may have a perovskite-type lattice structure. The perovskite-type lattice structure is a relatively simple crystal structure, which contributes to the higher piezoelectric coefficients in materials with such a structure.
The piezoelectric material may be one or more of: (Bi,Na)TiC>3; (Ba,Ca)(Ti,Zr)03; or (K,Na)Nb03.
In some forms, the first conductive layer may comprise two or more substantially parallel rows of a first conductive material. In this manner, each row of the first conductive material may form an electrode. In some forms, the second conductive layer may comprise two or more substantially parallel columns of a second conductive material. Similarly, in this manner each column of the second conductive material may form an electrode.
In some forms, the rows of the first conductive material may be substantially perpendicular to the columns of the second conductive material. In this regard, the rows of the first conductive material and the columns of the second conductive material may at least partially intersect to form a hatched pattern. For example, the rows and columns may form a cross-hatched pattern.
In some forms, the sensing layer may comprise a plurality of discrete regions of the piezoelectric material. In this regard, the discrete regions of the piezoelectric material may substantially correspond to the regions at which the rows of the first conductive material and the columns of the second conductive material intersect. In this way, each discrete region of piezoelectric material is independent from each other discrete region, allowing contact to be sensed (i.e. detected) with a high degree of accuracy.
In some forms, the sensing layer may further comprise an insulating material surrounding the discrete regions of piezoelectric material. Suitable insulating materials may include condensed matter materials such as inorganic materials (e.g. S1O2, AI2O3, S13N4 or other inorganic materials), organic materials (e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials), composites or a combination thereof. This can assist in further isolating the discrete regions of piezoelectric material and improve accuracy of the contact sensor.
In some forms, the contact sensor may further comprise a second substrate, for example in the form of a cover. The type of cover, such as the material or format of the cover, may be dependent on the intended use of the contact sensor. For example, in some forms the cover may further comprise key pads to specifically identify regions of the contact sensor to be contacted. In other forms, the cover may be a thin panel or sheet, such as a thin film or glass sheet. This cover may protect the first conductive layer, sensing layer and second conductive layer from damage, and be the material that a user contacts (i.e. touches) when utilising the contact sensor disclosed herein.
In some forms, one or more of the first substrate, first conductive layer, sensing layer and second conductive layer may be substantially transparent. This may be dependent on the intended application of the contact sensor. For example, each of the first substrate, first conductive layer, sensing layer and second conductive layer may be substantially transparent in contact sensors for smart phone, tablet, laptop, etc., touchscreens. According to a second aspect, a contact sensor is disclosed. The contact sensor comprises a first insulating substrate, a first conductive layer, a sensing layer and a second conductive layer. The sensing layer comprises an inorganic lead-free piezoelectric material. The contact sensor of the second aspect may be otherwise as defined above in the first aspect.
According to a third aspect, a method of manufacturing a contact sensor is also disclosed. The method comprises providing a first substrate and forming a first conductive layer on the first substrate. The method also comprises forming a sensing layer comprising a piezoelectric material, and forming a second conductive layer.
In some forms, the piezoelectric material may be a lead-free piezoelectric material.
This is contrary to most piezoelectric based touchscreen systems, and offers environmental benefits. In some forms, the piezoelectric material may alternatively or additionally be an inorganic piezoelectric material, which usually has a higher piezoelectric coefficient (approximately one order of magnitude higher) than organic (e.g. polymer-based) piezoelectric materials. The piezoelectric coefficient describes the amount of electrical charge generated per applied force unit. As such, materials with higher piezoelectric coefficients will generate more electrical charge, resulting in a contact sensor with higher sensitivity and more accuracy.
In some forms, the piezoelectric material may have a perovskite-type lattice structure. The perovskite-type lattice structure is a relatively simple crystal structure, which contributes to the higher piezoelectric coefficients in materials with such a structure.
The piezoelectric material may be one or more of: (Bi,Na)TiC>3; (Ba,Ca)(Ti,Zr)03; or (K,Na)Nb03.
In some forms, a second substrate may be provided, such that the first conductive layer, sensing layer and second conductive layer are positioned between the first and second substrates. The second substrate may, in some forms, be in the form of a cover. The type of cover, such as the material or format of the cover, may be dependent on the intended use of the contact sensor. For example, in some forms the cover may further comprise key pads to specifically identify regions of the contact sensor to be contacted. In other forms, the cover may be a thin panel or sheet, such as a thin film or glass sheet. This cover may protect the first conductive layer, sensing layer and second conductive layer from damage, and be the material that a user contacts (i.e. touches) when utilising the contact sensor disclosed herein. In some forms, the second conductive layer may be formed on the second substrate. The first and/or second substrate may be cleaned or otherwise treated to improve the wettability of its surface. For example, the substrate may be UV-treated to reduce its surface energy. It should be appreciated that other surface treatments may be employed to achieve improved wettability, and such surface treatment may be dependent on the type of substrate employed (e.g. glass, polyimide, polyester, etc.).
In some forms, the sensing layer may be formed on the first conductive layer (i.e. on the first conductive layer which has been formed on the first substrate). In other forms, the sensing layer may be formed on the second conductive layer (i.e. on the second conductive layer which has been formed on the second substrate). In yet other forms, some of the sensing layer may be formed on the first conductive layer (i.e. first substrate) and some of the sensing layer may be formed on the second conductive layer (i.e. second substrate), with the two halves being combined to form the contact sensor.
In some forms, the first conductive layer may comprise two or more substantially parallel rows of a first conductive material. In this manner, each row of the first conductive material may form an electrode.
In some forms, the second conductive layer may comprise two or more substantially parallel columns of a second conductive material. Similarly, in this manner each column of the second conductive material may form an electrode.
As will be appreciated by those skilled in the art, reference herein to a first conductive material and a second conductive material is primarily to assist with describing the different layers of materials required to form the contact sensor, and is not intended to imply that they are different materials. For example, the first and second conductive materials may be the same materials. For example, the conductive material may include a variety of transparent conductive oxide materials, such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), and some conductive polymers. Such transparent conductive oxide materials may be deposited onto the first substrate utilising relatively simple techniques such as various printing processes. This can allow contact sensors and, therefore, touchscreen panels significantly larger than known touchscreens to be manufactured. The transparent conductive oxide materials may be quantum oxide dots, and may be in the form of an ink as disclosed in co-pending PCT application number PCT/AU2016/050686, by the present applicant.
In some forms, the rows of the first conductive material may be substantially perpendicular to the columns of the second conductive material. In this regard, the rows of the first conductive material and the columns of the second conductive material may at least partially intersect to form a hatched pattern. For example, the rows and columns may form a cross-hatched pattern.
In some forms, a plurality of discrete regions of the piezoelectric material may be formed, thereby forming the sensing layer. In this regard, the discrete regions of the piezoelectric material may be formed to substantially correspond to the regions at which the rows of the first conductive material and the columns of the second conductive material intersect. In this way, each discrete region of piezoelectric material is independent from each other discrete region, allowing contact to be sensed (i.e. detected) with a high degree of accuracy.
In some forms, forming the sensing layer may further comprise surrounding the discrete regions of piezoelectric material with an insulating material. Suitable insulating materials may include condensed matter materials such as inorganic materials (e.g. S1O2, AI2O3, S13N4 or other inorganic materials), organic materials (e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials), composites or a combination thereof. This can assist in further isolating the discrete regions of piezoelectric material and improve accuracy of the contact sensor.
In some forms, forming the sensing layer may further comprise annealing the piezoelectric material. Annealing the piezoelectric material may improve its crystallinity and piezoelectric properties. Annealing may be conducted at a temperature between
approximately 50°C and approximately 550°C, although it should be appreciated that annealing may be conducted at a higher temperature, depending on the substrate material, piezoelectric material, etc. In this regard, substrate material choice may also need to be taken into consideration to ensure that the substrate will not be adversely affected by the annealing process. For example, in forms where the contact sensor comprises both first and second substrates, the substrates may be different materials. One of the substrate materials may have properties making it more suitable to undergo annealing. In such cases, the piezoelectric material may be formed on the conductive layer on that substrate (e.g. the second conductive layer may be formed on the second substrate, or the first conductive layer may be formed on the first substrate, with the piezoelectric material being subsequently formed thereon).
In forms where the sensing layer also comprises an insulating material surrounding the piezoelectric material, the piezoelectric material may be annealed prior to being surrounded with the insulating material. This may be preferred when the insulating material has a low melting temperature, to avoid its structure from undergoing any significant transformation (e.g. which may result in an otherwise transparent material becoming cloudy and opaque).
The first conductive layer, the sensing layer, the second conductive layer may be formed by any suitable process. For example, the respective layers may be formed by one or more of: ink-jet printing; spray printing; spin-coating; slot die coating; doctor blade coating; knife printing; screen-printing/coating; gravure printing/coating; engraved roller
printing/coating; comma-bar printing/coating; micro-roller printing/coating; nano-imprint printing; bar spreading; dip-coating; contact coating; non-contact coating; or a combination thereof. The forming process may be dependent on the material used in each of the respective layers. It should also be appreciated that each respective layer may be formed by the same process, or a different process.
In forms where the sensing layer comprises discrete regions of a piezoelectric material surrounded by an insulating material, each of the piezoelectric material and insulating material may be formed by one of the processes identified above.
Various embodiments of the method disclosed herein may provide a low-cost manufacturing method whereby patterning and deposition of various components of the contact sensor can be achieved using low-cost, readily available technologies that do not place size constraints on the manufactured sensor. Various embodiments may also provide a method that eliminates the requirement of laser cutting, irradiation, or adhesion layers which may adversely affect properties of the substrate and/or contact sensor.
According to a fourth aspect, a composition comprising a lead-free piezoelectric material dispersed in a solvent is also disclosed. The composition may be utilised as an ink in the printing of lead-free piezoelectric materials. For example, the ink may be applied using: ink-jet printing; spray printing; spin-coating; slot die coating; doctor blade coating; knife printing; screen-printing/coating; gravure printing/coating; engraved roller printing/coating; comma-bar printing/coating; micro-roller printing/coating; nano-imprint printing; bar spreading; dip-coating; contact coating; non-contact coating; or a combination thereof.
In some forms, the piezoelectric material may alternatively or additionally be an inorganic piezoelectric material. In some forms, the piezoelectric material may have a perovskite-type lattice structure. The piezoelectric material may be one or more of:
(Bi,Na)Ti03; (Ba,Ca)(Ti,Zr)03; or (K,Na)Nb03.
The composition disclosed in this fourth aspect may be utilised in the method of manufacturing a contact sensor as defined in the third aspect, or may be used to form the piezoelectric material of the sensing layer as defined in the first and second aspects. Brief Description
Notwithstanding any other forms that may fall within the scope of the contact sensor, method of manufacturing a contact sensor and composition as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 shows an exploded schematic illustration of an embodiment of a contact sensor according to the present disclosure;
Figure 2 shows a schematic top view illustration of an embodiment of a contact sensor, as shown in Figure 1 ;
Figure 3A shows a cross-sectional schematic illustration, taken along line A-A, of the contact sensor shown in Figure 2;
Figure 3B shows a cross-sectional schematic illustration, taken along line B-B, of the contact sensor shown in Figure 2; and
Figure 4 shows an exploded schematic illustration of an alternative embodiment of a contact sensor according to the present disclosure;
Figure 5 shows an exploded schematic illustration of an alternative embodiment of a contact sensor according to the present disclosure;
Figure 6 shows a schematic top view illustration of an embodiment of a contact sensor, as shown in Figure 5;
Figure 7A shows a cross-sectional schematic illustration, taken along line A-A, of the contact sensor shown in Figure 6;
Figure 7B shows a cross-sectional schematic illustration, taken along line B-B, of the contact sensor shown in Figure 6;
Figure 8 shows an exploded schematic illustration of an alternative embodiment of a contact sensor according to the present disclosure;
Figure 9 shows the optical transmission spectrum of a piezoelectric thin film deposition on ITO coated glass substrate;
Figure 10 shows a piezoelectric response butterfly loop of a typical perovskite- structured piezoelectric thin film;
Figure 11 shows a cross-sectional TEM image of a typical perovskite-structured piezoelectric thin film;
Figure 12 shows a ferroelectric P-E hysteresis loop a typical perovskite-structured piezoelectric thin film; Figure 13 shows a frequency-dependent dielectric constant of a typical perovskite- structured piezoelectric thin film.
Detailed Description
Referring firstly to Figure 1, a general exploded schematic illustration of an embodiment of a contact sensor is shown. In this embodiment the contact sensor is in the form of a touchscreen panel 100. Touchscreen panels may find particular application in smart phones, tablets, laptops, computers, automobile navigation systems, bank automatic teller machines (ATMs), industrial control systems, medical devices, ticket vending machines, etc.
The piezoelectric touchscreen panel 100 is shown having four rows 101 of a first conducting material, forming the first (or lower) conducting layer 102 on a substrate 104. The first conducting material may include indium tin oxide (ITO), or one of the other conducting materials disclosed in the Summary, such as fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers. The substrate 104 may be composed of condensed matter materials such as glass, silicon, polymers (e.g. polyimide, polyester, etc.), composites or another insulating material.
Above the first conducting layer 102, a sensing layer 106 is shown comprising an array of discrete regions of piezoelectric material 108 embedded in an insulating material 110. The piezoelectric material in the illustrated form may be an inorganic, lead-free piezoelectric material having a perovskite-type lattice structure, such as (Bi,Na)Ti03, (Ba,Ca)(Ti,Zr)03, or (K,Na)Nb03. The insulating material 110 may include inorganic materials (e.g. S1O2, AI2O3, S13N4 or other inorganic materials), organic materials (e.g. polyethylene terephthalate (PET), polyimide, epoxy resins or other organic materials), composites or a combination thereof.
The piezoelectric touchscreen panel 100 is also shown having four columns of a second conducting material, forming the second (or upper) conducting layer 112. Like the first conducting material, the second conducting material may comprise indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers. In this embodiment, the first and second conducting materials are the same, such as ITO. However in alternative embodiments the conducting materials may differ from one another.
Above the second conducting layer 112, the piezoelectric touchscreen panel 100 comprises a second substrate, in the form of a cover or screen 114. The screen 114 is the part of the touchscreen 100 that a user will contact.
As best shown in Figure 2, each row of the first conducting material in the first conducting layer 102 is substantially parallel to adjacent rows. Similarly, each column of the second conducting material in the second conducting layer 112 is substantially parallel to adjacent columns. Further, each row in the first conducting layer 102 is substantially perpendicular to each column in the second conducting layer 112, forming the hatched pattern (i.e. cross-hatched pattern) shown in Figure 2.
Figure 2 also best shows the relative placement of the discrete regions of piezoelectric material 108 with respect to the first (lower) conducting layer 102 and the second (upper) conducting layer 112. In this regard, the discrete regions of piezoelectric material 108 are shown positioned at the points 114 that rows of the first conducting layer 102 and columns of the second conducting layer 112 intersect or overlap.
For ease of representation, the sensing layer 106 (discrete regions of piezoelectric material 108 embedded in an insulating material 110) is depicted in Figure 2 as terminating before each edge of the substrate 104. It should be appreciated that the sensing layer 106 may extend to each edge of the substrate, as depicted in Figures 3A and 3B, and that the sensing layer 106 may only be depicted in this manner in Figure 2 to assist with interpretation (e.g. due to the schematic being a two-dimensional representation).
In forming the piezoelectric touchscreen 100, glass substrate 104 may be treated, such as by UV irradiation, to improve the wettability of its surface by reducing its surface energy. A first ink, comprising ITO quantum oxide dots dispersed in a solvent, may be used to print, such as by ink-jet printing, the rows of the first conducting layer 102 onto the glass substrate 104.
Once the rows of the first conducting layer 102 have dried, a second ink, comprising a lead-free piezoelectric material dispersed in a solvent, may be used to print, such as by ink-jet printing, discrete regions of piezoelectric material 108 onto specific regions of the first conducting layer 102. The discrete regions of piezoelectric material 108 are allowed to dry, and then the substrate is heated to anneal the piezoelectric material to improve its crystallinity and piezoelectric properties. Once cooled, a third ink, comprising polyethylene terephthalate (PET), may be used to print, such as by ink-jet printing, the PET (i.e. insulating material 110) into the spacing surrounding the discrete regions of piezoelectric material 108, thereby embedding the piezoelectric material 108 in the insulating material 110 to form the sensing layer 106.
Once the insulating material 110 has dried the first ink, comprising ITO quantum oxide dots dispersed in a solvent, can again be used to print, such as by ink-jet printing, the conductive material to continue forming the sensor. This time, the first ink is used to print columns, that are perpendicular to the first conducting layer 102 and that overlie the discrete regions of piezoelectric material 108, of the second conducting layer 112 onto the sensing layer 106. Insulating material 110 electrically isolates the first conducting layer 102 from the second conducting layer 112, other than at the discrete regions of piezoelectric material 108 which are used to detect contact therewith.
A second substrate, in the form of a thin-film cover or screen 114, is provided on top of the second conducting layer 112, thereby forming the piezoelectric touchscreen 100.
Whilst not shown, each of the rows of the first conducting layer 102, and each of the columns of the second conducting layer 112 may be electrically connected to a controller or a logic unit.
Referring now to Figure 4, an alternative embodiment of a contact sensor, in the form of a piezoelectric touchscreen 200, is shown. Piezoelectric touchscreen 200 is essentially identical to the piezoelectric touchscreen 100 depicted in Figure 1 except for screen 212.
In this regard, piezoelectric touchscreen 200 is also shown having four rows of a first conducting material, such as ITO, forming the first (or lower) conducting layer 202 on a substrate, such as glass, 204. Above the first conducting layer 202, a sensing layer 206 is also shown comprising an array of discrete regions of piezoelectric material 208 embedded in an insulating material 210. Four columns of a second conducting material, forming the second (or upper) conducting layer 212, with each column being substantially perpendicular to the first conducting layer 102 and overlying the discrete regions of piezoelectric material 108 in sensing layer 106.
Unlike the screen 114 shown in Figure 1, screen 214 is shown having "key pads" 216 positioned to overlie the array of discrete regions of piezoelectric material 208 (i.e. above those regions of the second conducting layer 212 which overlie the discrete regions of piezoelectric material 208, when assembled). Such an arrangement may be useful for a relatively static system that only requires or allows a specific configuration of touches on the screen to be recognised. Referring now to Figures 5 through 7, an alternative embodiment of a contact sensor in the form of a touchscreen panel 300 is shown.
In this form of the contact sensor, the panel 300 comprises a first or lower layer 301 having a layer of conducting material 302 on a substrate 304. In this form the layer of conducting material 302 extends across the substrate 304. In alternative forms the conducting material may be located in stripes or sections or in any layout that suits the purpose.
Above the first conducting layer 302, a sensing layer 306 is shown comprising a layer of piezoelectric material 308 embedded in an insulating material 310.
Above the sensing later, a conducting layer 312 is shown. The conducting layer is in the form of discrete deposits of a conducting material. The material may comprise indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron- doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers.
Above the conducting layer 312, the piezoelectric touchscreen panel 300 comprises a second substrate, in the form of a cover or screen 314. The screen 314 is the part of the touchscreen 300 that a user will contact.
As shown best in Figure 6, the contact sensor of this embodiment may in some forms include a plurality of keypads or buttons 316 adapted to allow user contact.
A further alternative embodiment is shown in Figure 8. In this embodiment the upper contact layer includes a plurality of keypads or buttons 416.
In this form of the contact sensor, the panel 400 comprises a first or lower layer 401 having a layer of conducting material 402 on a substrate 404. In this form the layer of conducting material 402 extends across the substrate 404. In alternative forms the conducting material may be located in stripes or sections or in any layout that suits the purpose.
Above the first conducting layer 402, a sensing layer 406 is shown comprising a layer of piezoelectric material 408 embedded in an insulating material 410.
Above the sensing later, a conducting layer 412 is shown. The conducting layer is in the form of discrete deposits of a conducting material. The material may comprise indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminium-doped zinc oxide (AZO), boron- doped zinc oxide (BZO), strontium ruthenium oxide (SRO), or some conductive polymers.
Above the conducting layer 412, the piezoelectric touchscreen panel 400 comprises a second substrate, in the form of a cover or screen 414. The screen 414 is the part of the touchscreen 400 that a user will contact. Experimental Results
In this invention, piezoelectric thin films including perovskite oxides (e.g. (Bi, Na)Ti03; (Ba, Ca)(Ti, Zr)03; or (K, Na)Nb03), and more are deposited or printed on the indium tin oxide (ITO) coated substrates, such as glass, PET and others with non-contact methods such as Physical Vapor Deposition (e.g., RF sputtering, thermal evaporation, e-gun evaporation, pulsed laser deposition and more), Chemical Vapor Deposition (e.g. atomic layer deposition, MOCVD, PECVD and more), spin coating and various printing technologies and others, for Proof of Concept. These thin films are transparent in the wavelength range of 400 nm to 1000 nm.
A typical transmittance spectra measured from the sample fabricated in our lab with RF sputtering technology is shown in Figure 9, which shows the resulting optical transmission spectrum of a piezoelectric thin film deposition on ITO coated glass substrate. This demonstrates that the optical clarity is satisfactory for the requirements of the applications, such as use in touchscreens etc.
In this invention, a typical sample fabricated in our lab showing the piezoelectric response butterfly loop with a strong piezoelectric strain coefficient d33 > 80 pm/V has been achieved. This is shown in Figure 10. Given the reversible nature of piezoelectric effect, a large piezoelectric charge coefficient d33 > 80 pC/N can be deduced. This suggests the piezoelectric thin film will generate at least 80 pico-Coulomb electrical charge when subject to 1 Newton mechanical force, demonstrating the high sensitivity of the sample.
The cross-sectional TEM image shown in Figure 11 clearly shows the thickness of this sample is around 300 nm. The robust ferroelectric activity of this sample is confirmed by its well-defined P-E hysteresis as shown in Figure 12. This sample also possesses high dielectric constant at low frequencies, i.e. < ~ 100 kHz, as shown in Figure 13.
It will be understood to persons skilled in the art that many other modifications may be made without departing from the spirit and scope of the contact sensor, method of manufacturing a contact sensor and composition as disclosed herein.
In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word
"comprise" or variations thereof such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the contact sensor, method of manufacturing a contact sensor and composition as disclosed herein.

Claims

1. A contact sensor comprising:
- a first conductive layer;
- a sensing layer comprising a piezoelectric material
- a second conductive layer.
2. A contact sensor as claimed in claim 1 wherein the piezoelectric material is a lead- free piezoelectric material.
3. A contact sensor as claimed in claim 1 or 2 wherein the piezoelectric material is an inorganic piezoelectric material.
4. A contact sensor as defined in any of the preceding claims, wherein the first conductive layer and the second conductive layer are separated by the sensing layer.
5. A contact sensor as claimed in any of the preceding claims, wherein the first conductive layer comprises two or more substantially parallel rows of a first conductive material.
6. A contact sensor as claimed in any one of the preceding claims wherein the second conductive layer comprises two or more substantially parallel columns of a second conductive material.
7. A contact sensor as claimed in claim 6, when dependent on claim 5, wherein the rows of the first conductive material are substantially perpendicular to the columns of the second conductive material.
8. A contact sensor as claimed in claim 7 wherein the rows of the first conductive material and the columns of the second conductive material at least partially intersect to form a hatched pattern.
9. A contact sensor as claimed in any one of the preceding claims wherein the sensing layer comprises a plurality of discrete regions of the piezoelectric material.
10. A contact sensor as claimed in claim 9, when dependent on claim 8, wherein the discrete regions of the piezoelectric material substantially correspond to the regions at which the rows of the first conductive material and the columns of the second conductive material intersect.
11. A contact sensor as claimed in claim 9 or 10 wherein the sensing layer further comprises an insulating material surrounding the discrete regions of piezoelectric material.
12. A contact sensor as claimed in claim 1 1 wherein the insulating material is selected from one or more of: inorganic materials; organic materials; or composite materials.
13. A contact sensor as claimed in any one of claims 1 through 6 wherein one conductive layer comprises an array of discrete deposits of conductive material.
14. A contact sensor as claimed in any one of claims 1 through 6 wherein one conductive layer comprises a continuous layer of conductive material.
15. A contact sensor as claimed in any one of the preceding claims wherein the piezoelectric material has a perovskite-type lattice structure.
16. A contact sensor as claimed in any one of the preceding claims wherein the piezoelectric material is one or more of: (Bi,Na)Ti03; (Ba,Ca)(Ti,Zr)03; or (K,Na)NbC>3.
17. A method of manufacturing a contact sensor, the method comprising:
- providing a first substrate;
- forming a first conductive layer on the first substrate;
- forming a sensing layer comprising a piezoelectric material; and
- forming a second conductive layer.
18. A method as claimed in claim 17 further comprising: - providing a second substrate such that the first conductive layer, sensing layer and second conductive layer are positioned between the first and second substrates.
19. A method as claimed in claim 17 or 18, wherein:
- forming the first conductive layer;
- forming the sensing layer; and/or
- forming the second conductive layer,
comprises one or more of: ink-jet printing; spray printing; spin-coating; slot die coating; doctor blade coating; knife printing; screen-printing/coating; gravure printing/coating; engraved roller printing/coating; comma-bar printing/coating; micro-roller printing/coating; nano-imprint printing; bar spreading; dip-coating; contact coating; non-contact coating; or a combination thereof.
20. A method as claimed in any one of claims 17 to 19 wherein forming the first conductive layer comprises forming two or more substantially parallel rows of a first conductive material.
21. A method as claimed in any one of claims 17 to 20 wherein forming the second conductive layer comprises forming two or more substantially parallel columns of a second conductive material.
22. A method as claimed in claim 21, when dependent on claim 20, wherein the rows of the first conductive material are substantially perpendicular to the columns of the second conductive material.
23. A method as claimed in claim 22 wherein the rows of the first conductive material and the columns of the second conductive material are formed to at least partially intersect, forming a hatched pattern.
24. A method as claimed in any one of claims 17 to 23 wherein forming the sensing layer comprises forming a plurality of discrete regions of the piezoelectric material.
25. A method as claimed in claim 24, when dependent on claim 23, wherein the discrete regions of the piezoelectric material are formed to substantially correspond to the points of intersection of the rows of the first conductive material and the columns of the second conductive material.
26. A method as claimed in claim 24 or 25 wherein forming the sensing layer further comprises surrounding the discrete regions of piezoelectric material with an insulating material.
27. A method as claimed in any one of claims 17 to 26 wherein forming the sensing layer further comprises annealing the piezoelectric material.
28. A method as claimed in any one of claims 17 to 27 wherein the piezoelectric material is one or more of: (Bi,Na)Ti03; (Ba,Ca)(Ti,Zr)03; or (K,Na)Nb03.
29. A method as claimed in any one of claims 17 - 19 wherein forming one conductive layer comprises forming an array of discrete deposits of conductive material.
30. A method as claimed in any one of claims 17 through 19 wherein forming one conductive layer comprises forming a continuous layer of conductive material.
PCT/AU2017/051084 2016-10-05 2017-10-05 Piezoelectric contact sensor WO2018064722A1 (en)

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